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Full text of "Notes on Leptothorax bradleyi Wheeler and L. wheeleri M. R. Smith (Hymenoptera: Formicidae)."

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WX. Brown, Jr. 

COLLECTION 



Reprinted from Entomological News, Vol. LXIII, No. 3, March, 1952 

Printed in U. S. A. 

Notes on Leptothorax bradleyi Wheeler and 

L. wheeleri M. R. Smith (Hymenoptera : 

Formicidae) ' 

By E. O. Wilson, Department of Zoology and Entomology, 
University of Tennessee 

Distributional data published up to the present for the closely 
related species Leptothorax bradleyi and-L. wheeleri have out- 
lined ranges which appeared to be mutually exclusive. When 
I recently examined specimens of this complex from two local- 
ities in Alabama, I considered that they might approach inter- 
grades between the two species, thus indicating that the two 
were actually subspecies. However, when representative spec- 
imens were borrowed from most of the collections which have 
been made of these forms, it was quickly established that the 
Alabama material was typical bradleyi. Furthermore, the ranges 
of the two species were found to overlap through at least three 
states, definitely establishing them as distinct species. The 
following paper consists of the new distributional data and 
additional significant descriptions. 

Workers of the two species are most easily distinguished on 
the basis of sculpturing, but they also differ in alitrunk profile, 
in proportions of the propodeal spines, and in size. In the 
descriptions given below only the characters useful in com- 
parison are emphasized. 

Leptothorax wheeleri M. R. Smith - ^n-^-^^i^f^&iui.f - 

L. wheeleri M. R, Smith, Ann. Ent. Soc. Amer., Vol. 22, p. 
547, fig. 1 (1929). Workers and queens. 

Worker. Ten workers representing all available records 
showed the following measurements : alitrunk length 0.90 mm.- 
1.13 mm., mean 1.04 mm.; head length 0.83 mm.-1.02 mm., 
mean 0.91 mm. ; distance between the tips of the propodeal 

^ Appreciation is expressed to Dr. M. R. Smith, Dr. Arnold Van Pelt, 
Dr. A. C. Cole, and Mr. H. T. Vanderford for the loan of most of 
the material used in this study. 



68 ENTOMOLOGICAL NEWS [Mar., 1952 

spines 0.28 mm.-0.37 mm., mean 0.30 mm. ; le^^h of propodeal 
spines 0.17 mm.-0.22 mm., mean 0.18 mm. (^ measurements 
with maximum error of ±0.01 mm.) Alitrunks were measured 
in profile from the dorsal base of the pronotal collar to the 
dorsum of the junction with the petiole; heads were measured 
in profile from the anterior edge of the clypeus to the extreme 
occipital border. 

Dorsum of head covered by longitudinal rugae, the interspaces 
coarsely punctate,; the rugae extend forward past the fronto- 
clypeal suture as the clypeal carinae. Alitrunk coarsely rugo- 
reticulate. Petiole with distinct rugulae, fainter than those 
of the alitrunk. Postpetiole with a few faint rugulae, the 
interspaces punctate, the surface opaque. 

Alitrunk arcuate in profile, rising to its highest point at the 
pronotum. 

Localities. Specimens were examined from the following 
localities : Mississippi State College (M. R. Smith) ; Starkville, 
Miss. (M. R. Smith) ; War Trace, Tenn. (H. T. Vanderford) ; 
Greenbriar Cove, Great Smoky Mts. Nat. Park, Tenn. (A. C. 
Cole) ; Wilmington, N. C. (H. T. Vanderford) ; Dalton, Ga. 
(H. T. Vanderford) ; Gainesville, Fla. (T. H. Hubbell). Smith 
also recorded this species from Adaton, Miss., and L. G. and 
R. G. Wesson recorded it from South Central Ohio (Amer. 
Mid. Nat, Vol. 24, p. 96). 

Leptothorax bradleyi Wheeler 

L. bradleyi Wheeler, Psyche, Vol. 20, p. 113 (1913). Holotype 

worker. 

Worker. Ten workers representing all of the available 
records showed the following measurements: alitrunk length 
0.83 mm.-0.93 mm., mean 0.89 mm.; head length 0.70 mm.- 
0.80 mm., mean 0.74 mm. ; distance between the tips of the 
propodeal spines 0.25 mm.-0.28 mm., mean 0.27 mm. ; length 
of the propodeal spines 0.08 mm.-0.15 mm., mean 0.13 mm. 

Alitrunk evenly flattened in profile. 

Sculpturing of the head similar to that in L. wheeleri. The 
entire mesonotum except for the margins finely rugulo-reticulate, 
giving a granulose appearance at magnifications of 36 X and less. 



Ixiii] . ENTOMOLOGICAL NEWS 69 

The posterior edge of the pronotum similar to mesonotum, but 
the anterior half rugo-reticulate. This reticulum merges with 
the posterior rugulo-reticulum, and the latter decreases in size 
anteriad until its interspaces are distinguished only as broad 
punctures within the coarser, anterior reticulum. The margins 
of the mesonotum longitudinally rugose. The reticulum of the 
basal face of the propodeum fades posteriad into coarse punctula- 
tion. The petiole punctate, opaque; sculpturing of the post- 
petiole irregular, with very shallow punctures, feebly shining to 
subopaque. 

The colorations of L. bradleyi and L. wheeleri are nearly 
identical, a rich ferruginous red. In most of the bradleyi work- 
ers examined the posterior margins of the gastric segments are 
distinctly infuscate; this condition is absent in wheeleri. 

Queen. Alitrunk length 1.33 mm.; head length 0.86 mm. 
Differing from the Worker in the usual characters separating 
these two castes, in sculpturing, and in proportions of the 
propodeal spines. Mesonotal scutum and scutellum evenly 
flattened in profile, the posterior third of the scutellum sloping 
downward somewhat. The propodeal spines blunt and denti- 
form. Notaulices and parapsidal furrows absent. 

Head covered by relatively coarse, longitudinal rugae (ap- 
proximately thirty would be cut by a line drawn transversely 
across the center of the head) ; rugae variable in size, fre- 
quently anastomosing; the interspaces punctate. Central por- 
tion and collar of pronotum granulose, the pleural arms rugo- 
reticulate, with the two zones of sculpturing meeting abruptly. 
Mesothoracic scutum and epipleurites with finer, more evenly 
longitudinal rugae (approximately forty would be cut by a line 
drawn transversely across the center of the scutum) . Scutellum 
with smaller, less regular, and indistinct rugae. Anterior margin 
of the propodeum rugose, the remainder granulose. Sides of 
the alitrunk mostly granulose, with a few marginal rugae. 
Petiole and postpetiole with numerous shallow, confluent punc- 
tures and a few indistinct longitudinal rugae ; their surfaces feebly 
shining. The gaster without sculpturing, glabrous. 

This queen differs very little from the cotype queen of L. 



70 ENTOMOLOGICAL NEWS [Mar., 1952 

wheeleri loaned to me by Dr. Smith. It can be distinguished 
from Smith's specimen on the basis of the following characters : 
distinct transverse rugae present between the propodeal spines 
in wheeleri, absent in hradleyi; petiole and postpetiole opaque 
in wheeleri, feebly shining in bradleyi; propodeal spines fairly 
well developed in wheeleri, dentiform in bradleyi; and smaller 
size of bradleyi. Otherwise the two closely resemble one an- 
other in sculpturing, flattening of the alitrunk, infuscation of the 
posterior margins of the gastric segments (absent in wheeleri 
workers), and general habitus under low magnification. This 
convergence of characters seems to indicate that the queen caste 
has diverged more slowly than the worker caste. If this is true, 
it appears that the bradleyi worker more closely approaches the 
ancestral form, in weaker sculpturing, flattening of the alitrunk, 
coloration, etc. 

Male. Alitrunk length 1.23 mm.; head length 0.52 mm. 
Antennae 12- jointed, with the funicular segments gradually 
diminishing in size distally and not forming a distinct club. 
Notaulices (Mayrian Furrows) present and distinct, converg- 
ing directly behind the center of the mesonotum. Wings with 
greatly reduced venation, the following veins occurring in the 
forewing: Sc + R, Ri, Rsfi, Rs + M, Rsf^, Mfj, M 4-CuA, A, 
cu-a. Mfg, CuA, and A distad to cu-a present but faded and 
indistinct. In one of the two specimens examined a small cross- 
vein (2r?) extends from Rsi^ almost to the stigma. (See 
Brown and Nutting, Trans. Amer. Ent. Soc, Vol. 75, pp. 
113-132, for a discussion of homology.) Hindwing with two 
very faint, basal abscissae. Costal, median, submedian, and 
cubital cells present in the fore wing; discoidal cell absent. 

Most of head covered by longitudinal rugulae, the interspaces 
punctate, a condition approaching that of the worker ; rugae of 
occiput indistinct, with a transverse trend. Most of the alitrunk 
covered by longitudinal rugulae, but these are finer and more 
closely set than those of head; interspace punctulations not ap- 
parent. Propodeum covered by shallow, confluent punctures. 
Petiole, postpetiole, and gaster shining, largely free from sculp- 
turing. All of body except appendages jet black. Scape and 



Ixiii] ENTOMOLOGICAL NEWS 71 

femora dark brown; funiculus and distal portion of legs light 
brown. Wings faintly iridescent. 

Localities. Specimens were examined from the following 
localities : Bay Minette, Ala. (E. O. Wilson) ; Tuscaloosa, Ala. 
(E. O. Wilson and Ben Sanders, Jr.) ; Hoschton, Ga. (H. T. 
Vanderford) ; Gainesville, Fla. (A. Van Pelt) ; Lake Placid, 
Fla. (T. C. Schneirla). The type locality is Billy's Island, 
Okefenokee Swamp, Ga. 

Knowledge of the biology of the two species is limited at 
present to scanty nesting data. Smith found, the several 
colonies comprising the type series of L. wheeleri in crevices 
and cavities of solid deciduous trees and under the bark of 
rotten pine stumps. Hubbs found his Florida wheeleri in gal- 
leries in a stick of solid pine firewood. The Wessons (Amer. 
Mid. Nat., Vol. 24, p. 96) found this species "in galleries in the 
hardened, weathered logs on old deserted and tumbledown log 
cabins exposed to the sun. Two other colonies were found 
on large oak trees where they were nesting in dead stobs." 
Most of the other specimens of both species have been collected 
as strays. My two colonies of L. bradleyi were found by chip- 
ping away the thick bark of living pines. Both were in flat, well 
defined galleries in the bark about three to five feet above the 
ground. The Tuscaloosa nest was carefully dissected, and what 
probably represents the bulk of the colony was collected; this 
contained one dealate queen, 42 workers, two males, and a 
small number of worker larvae and pupae.